Motor driving control device and motor driving control method

ABSTRACT

A rotational stop position of a motor is accurately controlled. A motor driving control device ( 100 ) includes a BEMF detection unit ( 118 ) for detecting zero-cross of back electromotive force of a motor coil provided in a motor, and a CPU ( 101 ) for controlling driving of the motor by a 1-phase energization method and, without a position sensor, performing commutation based on the zero-cross of the back electromotive force detected by the BEMF detection unit ( 118 ), controlling driving of the motor based on a rotational speed corresponding to a drive voltage and a load, and performing extension control of a commutation time for each step from a calculated deceleration start step until the rotational speed of the motor decreases to a predetermined rotational speed or less for enabling the motor to stop at a desired stop position when the driving of the motor is stopped.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of InternationalPatent Application No. PCT/JP2017/028892 filed on Aug. 9, 2017, whichclaims the benefit of Japanese Patent Application No. 2016-171243, filedon Sep. 1, 2016. The contents of these applications are incorporatedherein by reference in their entirety.

BACKGROUND Technical Field

The present disclosure relates to a motor driving control device and amotor driving control method suitable for controlling a rotational stopposition of a motor.

Background

Conventionally, when a stepping motor is subjected to positionsensorless driving for performing commutation with the zero-cross ofback electromotive force set as a trigger under 1-phase excitation, themotor rotates with a load current and a rotational speed correspondingto a drive voltage and a load. When driving of this motor is stopped,overrun occurs due to the inertia of the motor and positional accuracyof the rotational stop position of the motor is deteriorated.

When all switching elements (FETs) of a driving circuit (H-bridgecircuit) are turned off to stop the motor, the back electromotive forceperiodically changes with stoppage of the motor, and it is observed thatthe motor is rotating with the inertia of the motor.

In a hold current decay control method for performing control to stopthe motor so as to set a hold current to a high current under 2-phaseexcitation simultaneously with stoppage of the motor, gradually decreasethe current and stop the decrease of the current at a stable point ofthe 2-phase excitation, when the rotational speed of the motor is lowand thus the inertia is small, it is possible to secure positionalaccuracy. However, when the rotational speed of the motor is high andthus the inertia is large, the current periodically changes withstoppage of the motor during the control to stop the motor, and it canbe observed that the motor is rotating with the inertia of the motor.

For this reason, when an excessive current occurs during the foregoinghold current decay control to stop the motor, it is more possible tosecure positional accuracy by using fast decay control for applying avoltage in a reverse direction so as to consume the current as comparedwith the hold current decay control, but it is impossible to securepositional accuracy in the case of the inertia of a motor exceeding onequadrant of an electrical angle.

For example, a control method for a stepping motor capable of accuratelycontrolling the stop position of a rotor even when the rotational speedis high is disclosed in Japanese Patent Application Laid-Open No.2005-229743.

The control method of Japanese Patent Application Laid-Open No.2005-229743 is open control of 1-phase excitation, and the rotationalspeed just before the stop is arbitrary but fixed. The open control of1-phase excitation cannot achieve an optimum rotational speedcorresponding to a load, and a time in which vibration of the motor hassubsided varies according to the load. Since the rotational speed justbefore the stop of the motor is not stabilized due to the drive voltageor the load, the position sensorless driving may have a risk such thatit is difficult to accurately control the rotational stop position dueto occurrence of overrun caused by the inertia, etc. when a holding timeis extended in one step just before the stop. That is, it isinsufficient to control the rotational stop position of the motor to adesired stop position in a short period of time under some rotationalstates.

Therefore, the present disclosure is related to providing a motordriving control device and a motor driving control method capable ofaccurately controlling a rotational stop position of a motor in a shorttime.

SUMMARY

According to a first aspect of the present disclosure, a motor drivingcontrol device comprises a zero-cross detection unit configured todetect zero-cross of back electromotive force of a motor coil providedin a motor, and a control unit configured to control driving of themotor by a 1-phase excitation method and without a position sensorperform commutation based on the zero-cross of the back electromotiveforce detected by the zero-cross detection unit, control driving of themotor based on a rotational speed corresponding to a drive voltage and aload, and perform extension control of a commutation time for each stepfrom a calculated deceleration start step until the rotational speed ofthe motor decreases to a predetermined rotational speed or less forenabling the motor to stop at a desired stop position when the drivingof the motor is stopped.

Other units will be described in the detailed description ofembodiments.

According to the present disclosure, with respect to the motor drivingcontrol device and the motor driving control method, the rotational stopposition of the motor can be accurately controlled in a short time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall block diagram of a motor control system accordingto the present embodiment and a comparative example.

FIG. 2 is a detailed block diagram of a motor driving control deviceaccording to the present embodiment and the comparative example.

FIGS. 3A to 3D are first explanatory diagrams of an operation mode of anH-bridge circuit.

FIGS. 4E and 4F are second explanatory diagrams of the operation mode ofthe H-bridge circuit.

FIG. 5 is a waveform diagram illustrating currents/voltages of X-phaseand Y-phase of an H-bridge circuit of a comparative example.

FIG. 6 is a waveform diagram illustrating a commutation order of theH-bridge circuit of the comparative example.

FIG. 7 is a flowchart illustrating processing of a first quadrant of theX-phase in the comparative example.

FIG. 8 is a flowchart illustrating processing of a second quadrant ofthe X-phase in the comparative example.

FIG. 9 is a waveform diagram illustrating currents/voltages of theX-phase and the Y-phase of the H-bridge circuit in the presentembodiment.

FIG. 10 is a waveform diagram illustrating a commutation order of theH-bridge circuit in the present embodiment.

FIG. 11 is a flowchart illustrating processing of a first quadrant ofthe X-phase in the present embodiment.

FIG. 12 is a flowchart illustrating processing of a PWM cycle on anenergization side in the present embodiment.

FIG. 13 is a flowchart illustrating processing of a PWM cycle on a backelectromotive (non-energization) side in the present embodiment.

FIG. 14 is a graph illustrating a first deceleration example in thepresent embodiment.

FIG. 15 is a graph illustrating a second deceleration example in thepresent embodiment.

DETAILED DESCRIPTION

An embodiment for implementing the present disclosure will be describedhereinafter in detail with reference to the drawings.

FIG. 1 is an overall block diagram of a motor control system accordingto the present embodiment and a comparative example.

In FIG. 1, a stepping motor 120 is a bipolar type two-phase steppingmotor, and includes a rotor 126 having a permanent magnet and beingprovided rotatably and stators provided at positions quadrisectioned ina circumferential direction around the rotor 126. These stators includestators 122XP and 122XN of the X-phase, and stators 122YP and 122YN ofthe Y-phase. A winding is wound around each of these stators. Thewindings wound around the stators 122YP and 122YN are connected to eachother in series, and the combination of both the windings is referred toas a “stator winding 124Y”. Likewise, the windings wound around thestators 122XP and 122XN are connected to each other in series, and thecombination of both the windings is referred to as a “stator winding124X”. The stator windings 124Y and 124X are examples of motor coils.

A host device 130 outputs a speed command signal for commanding therotational speed of the stepping motor 120. A motor driving controldevice 100 controls driving of the stepping motor 120 according to thespeed command signal. H-bridge circuits 20X and 20Y each including acombination of half bridges connected to the stator windings areprovided to the motor driving control device 100, and apply an X-phasevoltage VMX and a Y-phase voltage VMY to the stator windings 124X and124Y, respectively.

The H-bridge circuit 20X is connected to the winding (an example of themotor coil) of the X-phase stator 122XN via a connection point Mout0,and further connected to the winding (an example of the motor coil) ofthe X-phase stator 122XP via a connection point Mout1. A coil currentIMout1-0 is a current flowing from the connection point Mout1 to theconnection point Mout0.

The H-bridge circuit 20Y is connected to the winding (an example of themotor coil) of the Y-phase stator 122YP via a connection point Mout2,and further connected to the winding (an example of the motor coil) ofthe Y-phase stator 122YN via a connection point Mout3. A coil currentIMout3-2 is a current flowing from the connection point Mout3 to theconnection point Mout2.

(Motor Driving Control Device 100)

Thereafter, the motor driving control device 100 will be described indetail with reference to FIG. 2. The stator windings 124X and 124Y oftwo systems and H-bridge circuits 20X and 20Y of the two systems areshown in FIG. 1. However, these stator windings and these H-bridgecircuits are collectively shown as a stator winding 124 of one systemand an H-bridge circuit 20 of one system.

A CPU (Central Processing Unit) 101 (an example of a control unit)provided inside the motor driving control device 100 controls each unitvia a bus 106 based on a control program stored in ROM (Read OnlyMemory) 103. RAM (Random Access Memory) 102 is used as a work memory ofthe CPU 101. A timer 104 measures elapsed time from a reset timing underthe control of the CPU 101. An I/O port 105 receives and outputs signalsto and from the host device 130 and other external devices shown inFIG. 1. A bridge control unit 107 controls each unit of a bridge controlcircuit 110 based on a command from the CPU 101.

Here, the bridge control circuit 110 is formed as an integral integratedcircuit. In the bridge control circuit 110, a PWM (pulse widthmodulation) signal generator 113 generates a PWM signal and supplies thePWM signal to the H-bridge circuit 20 under the control of the bridgecontrol unit 107. FETs (Field-Effect Transistors) 2, 4, 6, and 8 andFETs 15 and 17 are included in the H-bridge circuit 20. In FIG. 2,terminals on the lower side of these FETs are source terminals, andterminals on the upper side of these FETs are drain terminals. The PWMsignal is an ON/OFF signal to be applied as a gate voltage to theseFETs.

The FETs 2 and 4 are connected to each other in series, a DC powersource 140 and a ground line 142 are connected to this series circuit,and a predetermined voltage MVdd is applied to the series circuit.Likewise, the FETs 6 and 8 are also connected to each other in series,and the voltage MVdd is also applied to the series circuit. Diodes 12,14, 16, and 18 are parasitic diodes for reflux, and are connected inparallel to the FETs 2, 4, 6, and 8. The FETs 15 and 17 are provided forcurrent detection and form current mirror circuits together with theFETs 4 and 8, respectively. As a result, currents proportional tocurrents flowing through the FETs 4 and 8 flow through the FETs 15 and17, respectively.

The voltage VMout0 at the connection point Mout0 of the FETs 2 and 4 isapplied to one end of the stator winding 124 of the motor. The voltageVMout1 at the connection point Mout1 of the FETs 6 and 8 is applied toanother end of the stator winding 124. Therefore, a motor voltage VMcorresponding to the difference between the voltage VMout0 and thevoltage VMout1 is applied to the stator winding 124. Actually, the motorvoltage VM is the X-phase voltage VMX and the Y-phase voltage VMY shownin FIG. 1.

A current detection unit 116 (an example of a current detection unit)detects the motor current flowing through the stator winding. Morespecifically, the current detection unit 116 measures current valuesflowing through the FETs 15 and 17 according to the current direction,thereby outputting a current measurement value Icoil of a currentflowing through the stator winding 124. A D/A converter 115 receives adigital value of a current reference value Iref from the bridge controlunit 107, and converts the digital value to an analog value. Acomparator 114 compares a current measurement value Icoil of the analogvalue with the current reference value Iref, outputs a “1” signal whenthe former is equal to or larger than the latter, and outputs a “0”signal in other cases.

Furthermore, the voltages VMout0 and VMout1 are also supplied to a BEMF(back electromotive force) detection unit 118 (an example of azero-cross detection unit). The BEMF detection unit 118 detectszero-cross of back electromotive force of the stator windings 124Y and124X provided in the stator of the stepping motor 120. That is, when themotor voltage VM is back electromotive force, the BEMF detection unit118 outputs a flag ZC according to switching (zero-cross) in the voltagedirection during a period when no voltage is applied from the H-bridgecircuit 20.

The CPU 101 controls the driving of the stepping motor 120 by a 1-phaseexcitation method and without a position sensor, performs commutationbased on the zero-cross of the back electromotive force detected by theBEMF detection unit 118, and performs the control of the driving of thestepping motor 120 at a rotational speed corresponding to the drivevoltage and the load. In addition, as described later, when stopping thedriving of the stepping motor 120, the CPU 101 controls extension of acommutation time for each step from a calculated deceleration start stepuntil the rotational speed of the stepping motor 120 decreases to apredetermined rotational speed or less. At the predetermined rotationalspeed or less, the stepping motor 120 can stop at a desired stopposition.

(Operation Mode of H-Bridge Circuit 20)

FIGS. 3A to 3D and FIGS. 4E and 4F are explanatory diagrams of operationmodes of the H-bridge circuit. The operation modes of the H-bridgecircuit 20 will be described with reference to these explanatorydiagrams.

FIG. 3A shows a case where two diagonally opposite FETs are set to an ONstate to increase the absolute value of a motor current flowing throughthe stator winding 124. In the example shown in FIG. 3A, the FETs 4 and6 are in the ON state while the FETs 2 and 8 are in an OFF state. InFIG. 3A, an increase of the absolute value of the motor current isindicated by black arrows. In this state, the motor current flows in adirection indicated by a broken line via the FET6→the stator winding124→the FET 4, and the motor current increases. This operation mode iscalled a charge mode.

Furthermore, when the current is slowly decayed from the state of FIG.3A, the FET 6 is turned off as shown in FIG. 3B. The FET 4 maintains theON state, and the FETs 2 and 8 maintain the OFF state. Then, a currentlooping through the FET 4, the diode 18 (the parasitic diode of the FET8) and the stator winding 124 flows as indicated by a broken line in thefigures. This current is decayed by the FET 4, the diode 18 (theparasitic diode of the FET 8) and the impedance of the stator winding124, but the decay speed is low. This operation mode is called anasynchronous slow decay mode. In FIG. 3B, decay of the motor current isindicated by outlined arrows.

Furthermore, as a variation of the slow decay mode, as shown in FIG. 3C,the FET 8 may be further turned on. At this time, a motor currentlooping through the FETs 4 and 8 and the stator winding 124 flows asindicated by broken lines in the figures. This current is decayed by theFETs 4 and 8 and the impedance of the stator winding 124, but the decayspeed is lower. This operation mode is referred to as a synchronous slowdecay mode. In FIG. 3C, decay of the motor current is indicated byoutlined arrows.

Even when the gate voltage of any one FET is set to OFF, the FET is keptin the ON state for a period of time due to the parasitic capacitance ofthe FET. For this reason, for example, when a state in which the FET 4is turned on and the FET 2 is turned off is instantaneously switched toa state in which the FET 4 is turned off and the FET 2 is turned on, theFETs 2 and 4 connected in series are instantaneously set to the ONstate, so that the voltage MVdd and the ground are short-circuited withrelation to each other and thus the FETs 2 and 4 are destroyed. In orderto protect such a situation, the H-bridge circuit 20 is set to a shootthrough protection mode as shown in FIG. 3D.

FIG. 3D shows the shoot through protection mode. In the shoot throughprotection mode, the FETs 2, 4, 6, and 8 are set to the OFF state. Whenthe charge mode of FIG. 3A is switched to the shoot through protectionmode of FIG. 3D, back electromotive force occurs in the stator winding124. Therefore, the motor current flows through the diode 18→the statorwinding 124→the diode 12 (the parasitic diode of the FET 2) in adirection indicated by a broken line.

In the shoot through protection mode of FIG. 3D, a power dissipationcorresponding to a forward voltage drop of the diodes 12 and 18 occurs,so that the decay speed of the motor current becomes largest.

Here, when the FET 2 is turned on, the mode transits to a flyback modeshown in FIG. 4E. The flyback mode is a mode in which the motor currentflows through the diode 18→the stator winding 124→the FET 2 in adirection indicated by a broken line. In the flyback mode, the decayspeed of the motor current becomes slightly more gradual than that inthe shoot through protection mode.

When all energy charged in the stator winding 124 in the flyback mode isreleased and then the FET 2 is turned off, the mode transits to a backelectromotive force/free mode shown in FIG. 4F.

The back electromotive force mode is a mode in which the FETs 2, 4, 6,and 8 are set to the OFF state, no current flows in the H-bridge circuit20, and back electromotive force occurs. The free mode is a mode afterthe FETs 2, 4, 6, and 8 are set to the OFF state, no current flows inthe H-bridge circuit 20, and back electromotive force crosses zero.

The 1-phase excitation driving of the two-phase stepping motor performscommutation in the order of X+ phase→Y+ phase→X− phase→Y− phase tosequentially shift from the first quadrant to the fourth quadrant asshown in FIG. 6 below, thereby energizing the coils phase by phase. Whenthe stepping motor 120 is rotated in the reverse direction, thecommutation is performed in the order of X+ phase→Y− phase→X− phase→Y+phase.

In a normal case where the coil current is within a maximum current, theH-bridge circuit 20 transits in the order of the charge mode→the shootthrough protection mode→the flyback mode→the free mode.

The CPU 101 repeats the charge mode and the slow decay mode as theoperation mode under current limitation of the H-bridge circuit 20.Furthermore, as the operation mode under current limitation of theH-bridge circuit 20, the CPU 101 causes the H-bridge circuit 20 totransit in the order of the shoot through protection mode, the flybackmode, and the free mode after repetition of the charge mode and the slowdecay mode at every PWM cycle.

That is, under current limitation, the H-bridge circuit 20 repeats thecharge mode and the slow decay mode at every PWM cycle, and thentransits in the order of the shoot through protection mode the flybackmode the free mode. By using the slow decay mode, the decay of currentbecomes smaller than that in the fast decay mode. Therefore, therotational driving force and the holding force of the motor aremaintained, and a current ripple caused by the repetition of the chargemode and the slow decay mode is reduced.

The slow decay mode is available in a case in which the processing isperformed by an asynchronous slow decay mode alone and a case in whichthe mode is shifted to a synchronous slow decay mode after theasynchronous slow decay mode.

The flyback mode is available in a case in which a kickback voltage isregenerated to a power source via a parasitic diode (shoot throughprotection mode) and a case where the FET on an upper side (a high side)of this route is turned on for regeneration to the power source (flybackmode).

FIG. 5 is a waveform diagram illustrating the currents/voltages of theX-phase and the Y-phase of the H-bridge circuit 20 of a comparativeexample. FIG. 6 is a waveform diagram illustrating the commutation orderof the H-bridge circuit 20 of the comparative example. Hereinafter, theoperation in each quadrant will be described with reference to FIGS. 5and 6.

<<First Quadrant: Time t10>>

At a time t10 in the first quadrant, the H-bridge circuit 20X of theX-phase shifts to the charge mode, and the H-bridge circuit 20Y of theY-phase shifts to the flyback mode. As shown in FIG. 6, the steppingmotor 120 is in the X+ phase, and the voltage VMout1 becomes the voltageMVdd.

In the H-bridge circuit 20X of the X-phase, in the charge mode, thevoltage VMout1 is switched to the voltage MVdd, and the voltage VMout0is switched to GND (ground) as shown in FIG. 5. The voltage MVdd isapplied to the X-phase stator winding 124X, and the X-phase coil currentIMout1-0 gradually increases.

When the absolute value of the X-phase coil current IMout1-0 exceeds apredetermined maximum current, the H-bridge circuit 20X switches fromthe charge mode to the slow decay mode at every PWM cycle, whereby theabsolute value of the coil current IMout1-0 is maintained at less thanthe maximum current.

A flyback pulse (kickback) occurring in an opposite direction to thedirection of a voltage applied in an immediately preceding fourthquadrant occurs in the H-bridge circuit 20Y of the Y-phase. The H-bridgecircuit 20Y shifts to the free mode when the flyback voltage falls andfurther the coil current IMout3-2 is equal to 0. The H-bridge circuit20Y shifts to the free mode at a time t11.

In the free mode, back electromotive force appears in a directionopposite to that of the kickback in the H-bridge circuit 20Y of theY-phase. The CPU 101 performs commutation with the zero-cross of thisback electromotive force voltage set as a trigger, and shifts to a nextsecond quadrant. The occurrence time of the kickback and the backelectromotive force vary according to the drive voltage of the motor,the driving load of the motor, and the rotational speed.

Note that the shoot through protection mode is inserted between therespective modes as required so that the upper and lower FETs of thehalf bridge are not turned on at the same time. As a result,through-current can be prevented.

<<Second Quadrant: Time t14>>

At a time t14 in the second quadrant, the H-bridge circuit 20X of theX-phase shifts to the flyback mode, and the H-bridge circuit 20Y of theY-phase shifts to the charge mode. As shown in FIG. 6, the steppingmotor 120 is in the Y+ phase, and the voltage VMout3 becomes the voltageMVdd.

As shown in FIG. 5, a flyback pulse (kickback) occurring in a directionopposite to the direction of a voltage applied in an immediatelypreceding first quadrant occurs in the H-bridge circuit 20X of theX-phase. The H-bridge circuit 20X shifts to the free mode when theflyback voltage falls and further the coil current IMout1-0 is equal to0. The H-bridge circuit 20X shifts to the free mode at a time t15.

In the free mode, back electromotive force appears in an oppositedirection to that of the kickback in the H-bridge circuit 20X of theX-phase. The CPU 101 performs commutation with the zero-cross of thisback electromotive force set as a trigger, and shifts to a next thirdquadrant. The occurrence time of the kickback and the back electromotiveforce vary according to the drive voltage of the motor, the driving loadof the motor, and the rotational speed.

Note that the shoot through protection mode is inserted between therespective modes as required so that the upper and lower FETs of thehalf bridge are not turned on at the same time. As a result,through-current can be prevented.

In the charge mode, the voltage VMout3 is switched to the voltage MVddand the voltage VMout2 is switched to the GND in the H-bridge circuit20Y of the Y-phase. The voltage MVdd is applied to the Y-phase statorwinding 124Y, and the Y-phase coil current IMout3-2 gradually increases.

When the absolute value of the Y-phase coil current IMout3-2 exceeds apredetermined maximum current, the H-bridge circuit 20Y switches fromthe charge mode to the slow decay mode at every PWM cycle, whereby theabsolute value of the coil current IMout3-2 is maintained at less thanthe maximum current.

<<Third Quadrant: Time t18>>

At a time t18 in the third quadrant, the H-bridge circuit 20X of theX-phase shifts to the charge mode. In the charge mode, the coil currentIMout1-0 flows in an opposite direction to that in the first quadrant.The H-bridge circuit 20Y of the Y-phase shifts to the flyback mode. Inthe flyback mode, the coil current IMout3-2 flows in an oppositedirection to that in the first quadrant. As shown in FIG. 6, thestepping motor 120 is in the X− phase, and the voltage VMout0 becomesthe voltage MVdd.

As shown in FIG. 5, in the H-bridge circuit 20X of the X-phase, thevoltage VMout1 is switched to GND, and the voltage VMout0 is switched tothe voltage MVdd. A voltage is applied to the X-phase stator winding124X in a direction opposite to that in the first quadrant so that theX-phase coil current IMout1-0 gradually increases in the directionopposite to that in the first quadrant.

A flyback pulse (kickback) occurring in a direction opposite to thedirection of a voltage applied in an immediately preceding secondquadrant occurs in the H-bridge circuit 20Y of the Y-phase. When theflyback voltage falls and further the coil current IMout3-2 is equal to0, the H-bridge circuit 20Y shifts to the free mode. The H-bridgecircuit 20Y shifts to the free mode at a time t19.

In the free mode, back electromotive force appears in a directionopposite to that of the kickback in the H-bridge circuit 20Y of theY-phase. The CPU 101 performs commutation with the zero-cross of thisback electromotive force set as a trigger, and shifts to a next fourthquadrant. The occurrence time of the kickback and the back electromotiveforce vary according to the drive voltage of the motor, the driving loadof the motor, and the rotational speed.

The operation in the third quadrant is similar to the operation in thefirst quadrant except for the direction in which the current flows.

<<Fourth Quadrant: Time t22>>

At a time t22 in the fourth quadrant, the H-bridge circuit 20X of theX-phase shifts to the flyback mode. The H-bridge circuit 20Y of theY-phase shifts to the charge mode. As shown in FIG. 6, the steppingmotor 120 is in the Y− phase, and the voltage VMout2 becomes the voltageMVdd.

As shown in FIG. 5, a flyback pulse (kickback) occurring in a directionopposite to the direction of a voltage applied in an immediatelypreceding third quadrant occurs in the H-bridge circuit 20X of theX-phase. The H-bridge circuit 20X shifts to the free mode when theflyback voltage falls and further the coil current IMout1-0 is equal to0. The H-bridge circuit 20X shifts to the free mode at a time t23

In the free mode, back electromotive force appears in a directionopposite to that of the kickback in the H-bridge circuit 20X of theX-phase. The CPU 101 performs commutation with the zero-cross of thisback electromotive force set as a trigger, and shifts to a next thirdquadrant. The occurrence time of the kickback and the electromotiveforce voltage vary according to the drive voltage of the motor, thedriving load of the motor, and the rotational speed.

In the charge mode, the voltage VMout3 is switched to GND and thevoltage VMout2 is switched to the voltage MVdd in the H-bridge circuit20Y of the Y-phase. The voltage MVdd is applied to the Y-phase statorwinding 124Y in a direction opposite to that of the second quadrant, andthe Y-phase coil current IMout3-2 gradually increases in a directionopposite to that in the second quadrant.

The operation in the fourth quadrant is similar to the operation in thesecond quadrant except for the direction in which the current flows.

<<Subsequent Quadrants>>

The H-bridge circuits 20X and 20Y perform operations similar to theoperations in the first to fourth quadrants while sequentially switchingthe operations.

FIG. 7 is a flowchart illustrating processing of the first quadrant ofthe X-phase in a comparative example.

In the first quadrant, the CPU 101 sets a maximum duty for each PWMcycle and sets a value in a delay timer (processing S10), and theH-bridge circuit 20X of the X-phase shifts to an energization period. Inthis energization period, the H-bridge circuit 20X of the X-phase shiftsto the charge mode.

The CPU 101 turns on the FET 2 on the high side (HS) of the connectionpoint Mout1, and further turns on the FET 8 on the low side (LS) of theconnection point Mout0 (processing S11). Subsequently, the CPU 101starts an energization timer (processing S12).

The CPU 101 determines whether a maximum time associated with theY-phase has elapsed (processing S13). When determining that the maximumtime associated with the Y-phase has not elapsed (processing S13→No),the CPU 101 determines zero-cross of back electromotive force of theY-phase (processing S14). When determining that the back electromotiveforce of the Y-phase does not cross zero (processing S14→No), the CPU101 returns to the processing S13.

When determining the zero-cross of the back electromotive force of theY-phase (processing S14→Yes), the CPU 101 subtracts the delay timer(processing S15). When determining that the delay timer is not equal to0 (processing S16→No), the CPU 101 returns to the processing S13.

When the delay time is equal to 0 (processing S16→Yes), the CPU 101turns off the FET 2 on the high side (HS) of the connection point Mout1and the FET 8 on the low side (LS) of the connection point Mout0, andterminates the energization period (processing S17).

When the CPU 101 determines in processing S13 that the maximum timeassociated with the Y-phase has elapsed (processing S13→Yes), the CPU101 executes the processing S17 and terminates the energization periodregardless of the determination of the zero-cross of the backelectromotive force of the Y-phase and the count value of the delaytimer.

After the energization period is terminated, the CPU 101 terminates theenergization timer, calculates the rotational speed based on the valueof the energization timer (processing S18), and ends the processing inthe first quadrant of the X-phase.

The processing in the second quadrant of the Y-phase is similar to theprocessing in the first quadrant of the X-phase. The processing in thethird quadrant of the X-phase is similar to the processing in the firstquadrant of the X-phase except that the direction of the voltage appliedto the stator winding 124X (see FIG. 1) is different.

The processing in the fourth quadrant of the Y-phase is similar to theprocessing in the first quadrant of the X-phase except that thedirection of the voltage applied to the stator winding 124Y (see FIG. 1)is different.

FIG. 8 is a flowchart illustrating processing of the second quadrant ofthe X-phase in the comparative example.

First, in the second quadrant, the CPU 101 sets a maximum time in thetimer (processing S30). The H-bridge circuit 20X of the X-phase shiftsto a flyback period. In the flyback period, the H-bridge circuit 20X ofthe X-phase shifts to the flyback mode.

In the flyback period, when the flyback mode is terminated (processingS32→No), the H-bridge circuit 20X shifts to a back electromotive forceperiod. During the back electromotive force period, the H-bridge circuit20X of the X-phase shifts to the back electromotive force mode. Thetermination of the flyback mode may be detected based on any of thefollowing: falling of the flyback voltage, zero-cross of the flybackvoltage, and zero-cross of the coil current.

Subsequently, in the back electromotive force period, when the backelectromotive force mode is terminated (processing S33→No), the H-bridgecircuit 20X shifts to a free period. In the free period, the H-bridgecircuit 20X of the X-phase shifts to the free mode. The termination ofthe back electromotive force mode may be detected based on zero-cross ofthe back electromotive force. When the back electromotive force does notexceed 0 V due to an overload, the termination of the back electromotiveforce mode may be detected based on lapse of the delay time from a peakof the back electromotive force (approximately twice the time from thestart of the back electromotive force mode to the peak, etc.) or a nextvoltage increase after the peak of the back electromotive force.

In the free period, when determining termination of the second quadrantof the X-phase (processing S34→Yes), the CPU 101 ends the processing ofthe second quadrant of the X-phase.

When the conditions of the processing S32 and S33 are satisfied and whenthe condition of the processing S34 is not satisfied, the CPU 101returns to the processing S31 and determines excess of the maximum time.When the timer has exceeded the maximum time (processing S31→Yes), theCPU 101 ends the processing of the second quadrant of the X-phaseregardless of the operation mode.

The processing of the second quadrant of the X-phase is similar to theprocessing of the third quadrant of the Y-phase. The processing of thefourth quadrant of the X-phase is similar to the processing of thesecond quadrant of the X-phase except that the direction of thezero-crossing voltage is different.

The processing of the third quadrant of the Y-phase is similar to theprocessing of the first quadrant of the Y-phase except that thedirection of the zero-crossing voltage is different.

FIG. 9 is a waveform diagram illustrating the currents/voltages of theX-phase and the Y-phase of the H-bridge circuit 20 in the presentembodiment. FIG. 10 is a waveform diagram illustrating the commutationorder of the H-bridge circuit 20 in the present embodiment. Hereinafter,the operation in each quadrant will be described with reference to FIGS.9 and 10.

<<First Quadrant: Time t40>>

At a time t40 in the first quadrant, the H-bridge circuit 20X of theX-phase shifts to the charge mode, and the H-bridge circuit 20Y of theY-phase shifts to the flyback mode. As shown in FIG. 10, the steppingmotor 120 is in the X+ phase, and the voltage VMout1 becomes the voltageMVdd.

As shown in FIG. 9, in the charge mode, the voltage VMout1 is switchedto the voltage MVdd and the voltage VMout0 is switched to GND in theH-bridge circuit 20X of the X-phase. The voltage MVdd is applied to theX-phase stator winding 124X, and the X-phase coil current IMout1-0gradually increases.

When the absolute value of the X-phase coil current IMout1-0 exceeds apredetermined maximum current, the H-bridge circuit 20X switches fromthe charge mode to the slow decay mode at every PWM cycle, whereby theabsolute value of the coil current IMout 1-0 is maintained at less thanthe maximum current.

A flyback pulse (kickback) occurring in a direction opposite to thedirection of a voltage applied in an immediately preceding fourthquadrant occurs in the H-bridge circuit 20Y of the Y-phase. The H-bridgecircuit 20Y shifts to the free mode when the flyback voltage falls andfurther the coil current IMout3-2 is equal to 0. The H-bridge circuit20Y shifts to the free mode at a time t41.

In the free mode, back electromotive force appears in a directionopposite to that of the kickback in the H-bridge circuit 20Y of theY-phase. The CPU 101 performs commutation with the zero-cross of thisback electromotive force set as a trigger and shifts to a next secondquadrant. The occurrence time of the kickback and the back electromotiveforce vary according to the drive voltage of the motor, the driving loadof the motor, and the rotational speed.

Note that the shoot through protection mode is inserted between therespective modes as required so that the upper and lower FETs of thehalf bridge are not turned on at the same time. As a result, thethrough-current can be prevented.

<<Second Quadrant: Time t44>>

At a time t44 in the second quadrant, the H-bridge circuit 20X of theX-phase shifts to the flyback mode, and the H-bridge circuit 20Y of theY-phase shifts to the charge mode. As shown in FIG. 10, the steppingmotor 120 is in the Y+ phase, and the voltage VMout3 becomes the voltageMVdd.

As shown in FIG. 9, a flyback pulse (kickback) occurring in a directionopposite to the direction of a voltage applied in an immediatelypreceding first quadrant occurs in the H-bridge circuit 20X of theX-phase. The H-bridge circuit 20X shifts to the free mode when theflyback voltage falls and further the coil current IMout1-0 is equal to0. The H-bridge circuit 20X shifts to the free mode at a time t45.

In the free mode, back electromotive force appears in a directionopposite to the direction of the kickback in the H-bridge circuit 20X ofthe X-phase. The CPU 101 performs commutation with the zero-cross ofthis back electromotive force set as a trigger, and shifts to a nextthird quadrant. The occurrence time of the kickback and the backelectromotive force vary according to the drive voltage of the motor,the driving load of the motor, and the rotational speed.

Note that the shoot through protection mode is inserted between therespective modes as required so that the upper and lower FETs of thehalf bridge are not turned on at the same time. As a result,through-current can be prevented.

In the charge mode, the voltage VMout3 is switched to the voltage MVddand the voltage VMout2 is switched to GND in the H-bridge circuit 20Y ofthe Y-phase. The voltage MVdd is applied to the Y-phase stator winding124Y, and the Y-phase coil current IMout3-2 gradually increases.

When the absolute value of the Y-phase coil current IMout3-2 exceeds apredetermined maximum current, the H-bridge circuit 20Y switches fromthe charge mode to the slow decay mode at every PWM cycle, whereby theabsolute value of the coil current IMout3-2 is maintained at less thanthe maximum current.

Hereinafter, deceleration stop control is being executed from adeceleration start step to a deceleration stop step. Here, the number ofdeceleration steps is 4. In the deceleration stop step, the steppingmotor 120 reaches a final stop speed. The deceleration start step iscalculated from the number of driving steps and the number ofdeceleration steps.

<<Third Quadrant: Time t48: Deceleration Start Step>>

At a time t48 in the third quadrant, the H-bridge circuit 20X of theX-phase shifts to the charge mode in a direction opposite to that in thefirst quadrant. The H-bridge circuit 20Y of the Y-phase shifts to theflyback mode in which the coil current IMout3-2 flows in a directionopposite to that in the first quadrant. The third quadrant is a step ofstarting deceleration of the stepping motor 120. As shown in FIG. 10,the stepping motor 120 is in the X− phase, and the voltage VMout0becomes the voltage MVdd.

As shown in FIG. 9, in the charge mode, the voltage VMout1 is switchedto GND and the voltage VMout0 is switched to the voltage MVdd in theH-bridge circuit 20X of the X-phase. A voltage is applied to the X-phasestator winding 124 X in a direction opposite to that in the firstquadrant, and the X-phase coil current IMout1-0 gradually increases in adirection opposite to that in the first quadrant. The operation in thethird quadrant is similar to the operation in the first quadrant exceptfor the direction in which the current flows.

A flyback pulse (kickback) occurring in a direction opposite to thedirection of a voltage applied in an immediately preceding secondquadrant occurs in the H-bridge circuit 20Y of the Y-phase. The H-bridgecircuit 20Y shifts to the free mode when the flyback voltage falls andfurther the coil current IMout3-2 is equal to 0. The H-bridge circuit20Y shifts to the free mode at a time 49.

In the free mode, back electromotive force appears in a directionopposite to the direction of the kickback in the H-bridge circuit 20Y ofthe Y-phase. The occurrence time of the kickback and the backelectromotive force vary according to the drive voltage of the motor,the driving load of the motor, and the rotational speed.

As will be described below, when the motor current detected by thecurrent detection unit 116 exceeds a predetermined current value duringa period from the deceleration start step to the stop, the CPU 101specifies the slow decay mode to the H-bridge circuits 20X and 20Y atevery PWM cycle.

Based on the time of an immediately preceding step measured by thetimer, a predetermined maximum speed, and the number of decelerationsteps, the CPU 101 calculates the time of a step of this decelerationstep turn. In place of the zero-cross of the back electromotive force,the CPU 101 performs commutation with this time set as a trigger, andshifts to a next fourth quadrant.

With the deceleration, the absolute value of the coil current IMout1-0of the X-phase may drastically increase. In this case, the H-bridgecircuit 20X prevents overcurrent by shifting to the slow decay modeunder current control at every PWM cycle. Here, the absolute value ofthe coil current IMout1-0 slightly increases after a time t50, but theH-bridge circuit 20X has not shifted to the slow decay mode.

Note that the shoot through protection mode is inserted between therespective modes as required so that the upper and lower FETs of thehalf bridge are not turned on at the same time. As a result,through-current can be prevented.

<<Fourth Quadrant: Time t52: Second Step of Deceleration>>

At a time t52 in the fourth quadrant, the H-bridge circuit 20X of theX-phase shifts to the flyback mode in a direction opposite to that inthe second quadrant. The H-bridge circuit 20Y of the Y-phase shifts tothe charge mode in a direction opposite to that in the second quadrant.This fourth quadrant is a second step of the deceleration of thestepping motor 120. As shown in FIG. 10, the stepping motor 120 is inthe Y-phase, and the voltage VMout2 becomes the voltage MVdd.

As shown in FIG. 9, in the charge mode, the voltage VMout3 is switchedto GND and the voltage VMout2 is switched to the voltage MVdd in theH-bridge circuit 20Y of the Y-phase. The voltage MVdd is applied to theY-phase stator winding 124Y in a direction opposite to that in thesecond quadrant, and the Y-phase coil current IMout3-2 graduallyincreases in a direction opposite to that in the second quadrant. Theoperation in the fourth quadrant is similar to the operation in thesecond quadrant except for the direction in which the current flows.

A flyback pulse (kickback) occurring in a direction opposite to thedirection of a voltage applied in an immediately preceding thirdquadrant occurs in the H-bridge circuit 20X of the X-phase. The H-bridgecircuit 20X shifts to the free mode when the flyback voltage falls andfurther the coil current IMout1-0 is equal to 0. The H-bridge circuit20X shifts to the free mode at a time t53.

In the free mode, back electromotive force appears in a directionopposite to the direction of the kickback in the H-bridge circuit 20X ofthe X-phase. The occurrence time of the kickback and the backelectromotive force vary according to the drive voltage of the motor,the driving load of the motor and the rotational speed.

As described below, when the motor current detected by the currentdetection unit 116 exceeds a predetermined current value during a periodfrom the deceleration start step to the stop, the CPU 101 specifies theslow decay mode to the H-bridge circuits 20X and 20Y at every PWM cycle.

From the time of an immediately preceding step measured by the timer, apredetermined maximum speed, and the number of deceleration steps, theCPU 101 calculates the time of a step of this deceleration step turn. Inplace of the zero-cross of the back electromotive force, the CPU 101performs commutation with this time set as a trigger, and shifts to anext first quadrant.

The absolute value of the Y-phase coil current IMout3-2 may drasticallyincrease due to deceleration. In this case, the H-bridge circuit 20Yprevents overcurrent by shifting to the slow decay mode under currentcontrol at every PWM cycle. Here, the absolute value of the coil currentIMout3-2 slightly increases after a time t54, but the H-bridge circuit20Y has not shifted to the slow decay mode.

Note that the shoot through protection mode is inserted between therespective modes as required so that the upper and lower FETs of thehalf bridge are not turned on at the same time. As a result,through-current can be prevented.

<<First Quadrant: Time t56: Third Step of Deceleration>>

At a time t56 in the first quadrant, the H-bridge circuit 20X of theX-phase shifts to the charge mode. The H-bridge circuit 20Y of theY-phase shifts to the flyback mode. This first quadrant is a third stepof deceleration of the stepping motor 120. As shown in FIG. 10, thestepping motor 120 is in the X+ phase, and the voltage VMout1 becomesthe voltage MVdd.

As shown in FIG. 9, in the charge mode, the voltage VMout0 is switchedto the voltage MVdd and the voltage VMout1 is switched to the GND in theH-bridge circuit 20X of the X-phase. The voltage MVdd is applied to theX-phase stator winding 124X, and the X-phase coil current IMout1-0gradually increases.

A flyback pulse (kickback) occurring in a direction opposite to thedirection of a voltage applied in an immediately preceding fourthquadrant occurs in the H-bridge circuit 20Y of the Y-phase. The H-bridgecircuit 20Y shifts to the free mode when the flyback voltage falls andfurther the coil current IMout3-2 is equal to 0. The H-bridge circuit20Y shifts to the free mode at a time t57.

In the free mode, back electromotive force appears in a directionopposite to the direction of the kickback in the H-bridge circuit 20Y ofthe Y-phase. The occurrence time of the kickback and the backelectromotive force vary according to the drive voltage of the motor,the driving load of the motor, and the rotational speed.

The operation in the first quadrant so far is similar to the operationin the third quadrant except for the direction in which the currentflows.

As described below, when the motor current detected by the currentdetection unit 116 exceeds a predetermined current value during theperiod from the deceleration start step to the stop, the CPU 101specifies the slow decay mode to the H-bridge circuits 20X and 20Y atevery PWM cycle.

From the time of an immediately preceding quadrant step measured by thetimer, a predetermined maximum speed, and the number of decelerationsteps, the CPU 101 calculates the time of a step of this decelerationstep turn. In place of the zero-cross of the back electromotive force,the CPU 101 performs commutation with this time set as a trigger, andshifts to a next fourth quadrant.

The absolute value of the X-phase coil current IMout1-0 may drasticallyincrease due to deceleration. In this case, the H-bridge circuit 20Xprevents overcurrent by shifting to the slow decay mode under currentcontrol at every PWM cycle. Here, the absolute value of the coil currentIMout1-0 slightly increases after a time t58, but the H-bridge circuit20X has not shifted to the slow decay mode.

Note that the shoot through protection mode is inserted between therespective modes as required so that the upper and lower FETs of thehalf bridge are not turned on at the same time. As a result,through-current can be prevented.

<<Second Quadrant: Time t60: Deceleration Stop Step>>

At a time t60 in the second quadrant, the H-bridge circuit 20X of theX-phase shifts to the flyback mode. The H-bridge circuit 20Y of theY-phase shifts to the charge mode. This second quadrant is adeceleration stop step of the stepping motor 120. As shown in FIG. 10,the stepping motor 120 is in the Y+ phase, and the voltage VMout3becomes the voltage MVdd.

As shown in FIG. 9, in the charge mode, the voltage VMout3 is switchedto the voltage MVdd, and the voltage VMout2 is switched to the GND inthe H-bridge circuit 20Y of the Y-phase. The voltage MVdd is applied tothe Y-phase stator winding 124Y, and the Y-phase coil current IMout3-2gradually increases. The operation in the second quadrant is similar tothe operation in the fourth quadrant except for the direction in whichthe current flows.

A flyback pulse (kickback) occurring in a direction opposite to thedirection of a voltage applied in an immediately preceding thirdquadrant occurs in the H-bridge circuit 20X of the X-phase. The H-bridgecircuit 20X shifts to the free mode when the flyback voltage falls andfurther the coil current IMout1-0 is equal to 0. The H-bridge circuit20X shifts to the free mode at a time t61.

In the free mode, back electromotive force appears in a directionopposite to the direction of the kickback in the H-bridge circuit 20X ofthe X-phase. The occurrence time of the kickback and the backelectromotive force vary according to the drive voltage of the motor,the driving load of the motor and the rotational speed.

As described below, when the motor current detected by the currentdetection unit 116 exceeds a predetermined current value during theperiod from the deceleration start step to the stop, the CPU 101specifies the slow decay mode to the H-bridge circuits 20X and 20Y atevery PWM cycle.

From the time of an immediately preceding quadrant step measured by thetimer, a predetermined maximum speed, and the number of decelerationsteps, the CPU 101 calculates the time of a step of this decelerationstep turn. In place of the zero-cross of the back electromotive force,the CPU 101 performs commutation with this time set as a trigger, andshifts to a next third quadrant.

The absolute value of the Y-phase coil current IMout3-2 may drasticallyincrease due to deceleration. In this case, the H-bridge circuit 20Yprevents overcurrent by shifting to the slow decay mode under currentcontrol at every PWM cycle. Here, since the absolute value of the coilcurrent IMout3-2 increases beyond a threshold value after a time t62,the H-bridge circuit 20Y periodically shifts to the slow decay mode.

As a result, the stepping motor 120 reaches a final stop speed, and canbe stopped at a desired stop position.

Note that it is also possible to decelerate by gradually decreasingON-duty from 100% within a range where the coil current does not affectthe driving of the motor and the final position holding. The ON-duty isa turn-on time of the FET at every PWM cycle. In this case, duringdeceleration under stop control, the commutation may be performed withthe zero-cross of the back electromotive force set as a trigger.Detection of step-out can be identified based on deviation of thekickback time or back electromotive force.

FIG. 11 is a flowchart illustrating processing of the first quadrant ofthe X-phase in the present embodiment. The present embodiment isdifferent from the comparative example shown in FIG. 7 in the processingafter the stop control start position. The CPU 101 sets a stop controltimer after the stop control start position, and further operates with astop control timer instead of the zero-cross of the back electromotiveforce of the Y-phase after (the stop control start position+1).

In the first quadrant, the CPU 101 sets a maximum duty for each PWMcycle and sets a value in the delay timer (processing S50). The H-bridgecircuit 20X of the X-phase shifts to the energization period. In thisenergization period, the H-bridge circuit 20X of the X-phase shifts tothe charge mode.

The CPU 101 turns on the FET 2 on the high side (HS) of the connectionpoint Mout1 and further turns on the FET 8 on the low side (LS) of theconnection point Mout0 (processing S51). Subsequently, the CPU 101starts an energization timer (processing S52).

The CPU 101 determines whether the rotational position of the motor isnot less than (the stop control start position+1) (processing S53). Whenthe rotational position is not less than (the stop control startposition+1) (processing S53→Yes), the CPU 101 starts the stop control.The CPU 101 subtracts the stop control timer (processing S58), repeatsthe processing S59 and the processing S58 until the timer value is equalto 0, and then proceeds to processing S60.

When the rotational position of the motor is less than (the stop controlstart position+1) (processing S53→No), the CPU 101 proceeds toprocessing S54 and performs normal first quadrant processing.

In processing S54, the CPU 101 determines whether the maximum timeassociated with the Y-phase has elapsed. When determining that themaximum time associated with the Y-phase has not elapsed (processingS54→No), the CPU 101 determines zero-cross of back electromotive forceof the Y-phase (processing S55). When determining that the backelectromotive force of the Y-phase has not crossed zero (processingS55→No), the CPU 101 returns to the processing S54.

When determining the zero-cross of the back electromotive force of theY-phase (processing S55→Yes), the CPU 101 subtracts the delay timer(processing S56). When determining that the delay timer is not equal to0 (processing S57→No), the CPU 101 returns to the processing S54.

When the energization timer is equal to 0 (processing S57→Yes), the CPU101 proceeds to processing S60, turns off the FET 2 on the high side(HS) of the connection point Mout1 and the FET 8 on the low side (LS) ofthe connection point Mout0, and terminates the energization period.

When determining in processing S54 that the maximum time associated withthe Y-phase has elapsed (processing S54→Yes), the CPU 101 executes theprocessing S60 and terminates the energization period irrespective ofthe determination as to the zero-cross of the back electromotive forceof the Y-phase and the count value of the delay timer.

After the termination of the energization period, the CPU 101 terminatesthe energization timer and calculates the rotational speed based on thevalue of the energization timer (processing S61). Furthermore, in thecase of the stop control start position or more (processing S62→Yes),the CPU 101 sets the stop control timer (processing S63). Then, the CPU101 ends the processing in the first quadrant of the X-phase.

The processing of the second quadrant of the X-phase by the motordriving control device according to the present embodiment is similar tothe processing of the comparative example shown in FIG. 8

FIG. 12 is a flowchart illustrating the processing of anenergization-side PWM cycle in the present embodiment.

Here, “energization” includes one or more “energization-side PWM cycles”executed at every PWM cycle. The processing of the energization-side PWMcycle is always necessary to perform maximum current limitation understop control including normal control. In the 1-phase excitationdriving, a method using no PWM cycle is general.

When the energization-side PWM cycle is started and it is an initialcycle of the PWM cycle in this quadrant (processing S70→Yes), the CPU101 sets a threshold value for the coil current (processing S71) andproceeds to processing S72. When the energization-side PWM cycle is notthe initial cycle of the PWM cycle in this quadrant (processing S70→No),the CPU 101 proceeds to processing S72.

When the coil current exceeds the threshold value (processing S72→Yes),the CPU 101 causes the H-bridge circuit 20 to shift to the slow decaymode (processing S73) and proceeds to processing S74.

When the coil current does not exceed the threshold value (processingS72→No), the CPU 101 proceeds to processing S74. When the H-bridgecircuit 20 is not in the slow decay mode (processing S74→No), the CPU101 shifts to the charge mode (processing S75), and when the H-bridgecircuit 20 is in the slow decay mode (processing S74→Yes), the CPU 101determines whether the energization-side PWM cycle terminates(processing S76).

The CPU 101 repeats these processes S72 to S75 until theenergization-side PWM cycle terminates (processing S76→No).

FIG. 13 is a flowchart illustrating the processing of the PWM cycle on aback electromotive side in the present embodiment. The backelectromotive side is a non-energization side of the PWM cycle, and theprocessing of the PWM cycle on this side is executed at every PWM cycle.

When the back electromotive side PWM cycle is started and it is aninitial cycle of the PWM cycle in this quadrant (processing S80→Yes),the CPU 101 causes the H-bridge circuit 20 to shift to the flyback mode(processing S81), and proceeds to processing of S82. When the backelectromotive side PWM cycle is not the initial cycle of the PWM cyclein this quadrant (processing S80→No), the CPU 101 proceeds to processingS82.

Thereafter, when the H-bridge circuit 20 is in the flyback mode(processing S82→Yes) and this flyback mode has terminated (processingS83→Yes), the H-bridge circuit 20 shifts to the back electromotive forcemode (processing S84), and then proceeds to processing S85. When theH-bridge circuit 20 is not in the flyback mode (processing S82→Yes), theH-bridge circuit 20 proceeds to processing S85. When the H-bridgecircuit 20 is in the flyback mode (processing S82→Yes) and this flybackmode continues (processing S83→No), the H-bridge circuit 20 proceeds toprocessing S88.

In processing S85, when the H-bridge circuit 20 is not in the backelectromotive force mode (processing S85→No) or when the backelectromotive force mode has terminated (processing S86→Yes), theH-bridge circuit 20 shifts to the free mode (processing S87), andproceeds to processing S88. When the H-bridge circuit 20 is in the backelectromotive force mode (processing S85→Yes) and the back electromotiveforce mode continues (processing S86→No), the H-bridge circuit 20proceeds to processing S88.

The CPU 101 and the H-bridge circuit 20 repeat these processes S82 toS87 until the energization-side PWM cycle has terminated (processingS88→No).

<<Various Deceleration Control Methods>>

In the motor driving control device 100 according to the presentembodiment, when stopping the driving of the stepping motor 120, the CPU101 performs extension control of a commutation time for each step fromthe calculated deceleration start step until the rotational speed of thestepping motor 120 decreases to a predetermined rotational speed or lessat which the stepping motor 120 can stop at a desired stop position.More specifically, when stopping the driving of the stepping motor 120,the CPU 101 performs deceleration control in which a phase switching(commutation) time is increased according to the following decelerationstep until the rotational speed reaches a speed capable of securingpositional accuracy of the rotational stop position of the steppingmotor 120, so that the positional accuracy can be secured with fewsteps.

<<Deceleration Control Method Based on Increase of Time>>

The CPU 101 ceases the commutation based on the zero-cross of the backelectromotive force until the stepping motor 120 reaches a predeterminedrotational speed or less from the deceleration start step, and extendsthe commutation time for each step. More specifically, the CPU 101measures the time of 1-phase excitation just before deceleration, andperforms time control by gradually extending the phase switching(commutation) time, thereby decelerating the rotational speed of themotor. This deceleration method can secure the positional accuracy byadjusting the number of deceleration steps and a time increasing rate.It may be considered to be increase of time, for example, to increasethe commutation time for each step at a constant rate (e.g., the time isextended by 25% in each step). This is represented in the followingexpression (1).[Expression 1]T _(next)(1+K _(extend))×T _(now)  (1)

Where,

T_(next): phase switching time in next step

T_(now): phase switching time in current step

K_(extend): time increasing coefficient between steps (for example, 25%or the like)

As a result, the time in each step is multiplied by 1.25→1.56→1.95→2.44,and the average speed is equal to 80%→64%→51.2%→41.0%. According to thisdeceleration method, the rotational speed can be steeply reducedimmediately after the start of deceleration with few steps, and therotational speed can be gradually reduced immediately before thetermination of deceleration.

<<Deceleration Control Method Based on Specification of FinalSpeed+Constant Speed Decrease>>

The time of 1-phase excitation just before the deceleration start stepis measured, and the speed is calculated by the expression (2).[Expression 2]V _(first)=1/T _(prev)  (2)

Where,

V_(first): speed just before deceleration start step

T_(prev): time of 1-phase excitation just before deceleration start step

Furthermore, the number of deceleration steps and the final step timeare specified, and calculation is performed according to the expression(3) so that the decrease in the average speed between steps is constant.[Expression 3]V _(tick)=(V _(first)−1/T _(final))/D _(steps)  (3)

Where,

V_(tick): decrease of speed between steps

D_(steps): the number of deceleration steps

V_(first): speed at deceleration start time

T_(final): final step time

The speed in each step can be calculated by substituting this speeddecrease into the expression (4).[Expression 4]V _(next) =V _(now) −V _(tick)  (4)

Where,

V_(next): speed in next step

V_(now): speed in current step

V_(tick): speed decrease between steps

According to this deceleration method, it is possible to performsettings for efficiently preventing overrun by specifying the rotationalspeed mainly contributing to kinetic energy.

<<Deceleration Control Method Based on Specification of FinalSpeed+Constant Time Increase>>

This is a method of specifying the number of deceleration steps and thetime of a final step so that the time increasing rate of each step isconstant. The relationship between the rotational speed and the timeaccording to this deceleration control method is shown in FIG. 14.

This deceleration control method has a characteristic such that decreasein average speed immediately after deceleration starts is substantialand decrease in average speed decrease immediately before decelerationterminates is slight.

<<Deceleration Control Method Based on Specification of FinalSpeed+Constant Deceleration>>

This is a method of specifying the number of deceleration steps and therotational speed of a final step so that the deceleration is constant.At this time, the rotational speed is represented by a linear functionof time. The relationship between the rotational speed and the timeaccording to this deceleration control method is shown in FIG. 15.

<<Deceleration Control Method Based on Specification of FinalSpeed+Speed Table>>

The commutation time is specified from a speed calculated from adeceleration obtained by measuring the time of 1-phase energization justbefore the deceleration start step, specifying the deceleration stepnumber and the final step time, and performing ratio calculation basedon a speed table (trapezoid/S-shape, presence or absence of a linearpart), and deceleration is performed. According to this decelerationmethod, the speeds immediately after the deceleration starts andimmediately before the deceleration terminates become gradual, and theinfluence on the load becomes slightest.

In addition to the deceleration control method described above, themotor rotational speed may be reduced by simultaneously using dutycontrol to intentionally gradually reduce the duty per PWM cycle of1-phase energization. For example, the duty is reduced by 10% each time,so that the duty is reduced to 90%→80%→70%→60%. In this case, when thecommutation is performed with the zero-cross of the back electromotiveforce set as a trigger, for example, in a case where the load increasesdue to the rotation of the motor, the current required for lifting theload may be insufficient, and therefore time control of graduallyextending the phase switching (commutation) time may be used incombination. The effect of this duty control on the deceleration of thespeed is different depending on the motor and voltage/load.

Effect of the Present Embodiment

(1) By performing the extension control of the commutation time for eachstep or the extension control of the zero cross interval between thesteps, it is possible to enhance the positional accuracy of therotational stop position of the motor when the motor driven under1-phase energization and without a position sensor is stopped withrespect to a varying voltage or a load varying due to rotation of themotor.(2) According to the deceleration control method of the presentembodiment, it is possible to stop the motor at a desired stop positionwithout overrunning the rotational stop position of the motor.(3) According to the deceleration control method of the presentembodiment, it is possible to accurately control the rotational stopposition of the motor with a low number of steps and in a short timeirrespective of the drive voltage or the load.(4) When the coil current exceeds the threshold value, the CPU 101specifies the slow decay mode at the PWM cycle. As a result, the decayof the coil current can be suppressed, and the driving force and theholding force can be maintained. In addition, generation ofelectromagnetic noise can be suppressed.(5) When the coil current exceeds the threshold value, the CPU 101performs control so as to repeat the charge mode and the slow decaymode. This reduces the current ripple.

Variant

The present disclosure is not limited to the above embodiment, and maybe modified and implemented without departing from the subject matter ofthe present disclosure. For example, the following matters (a) to (c)may be adopted.

(a) The type of the motor is not limited to the stepping motor, butincludes a brushless DC motor.

(b) It is also possible to perform deceleration by gradually reducingthe on-duty from 100% within a range where the coil current does notaffect the driving of the motor and the final position holding. Notethat the on-duty means the time an FET at each PWM cycle is turned on.(c) the CPU 101 may perform the extension control of the commutationtime for each step by setting a stop control value in an energizationtimer without the stop control timer.

What is claimed is:
 1. A motor driving control device comprising: azero-cross detection unit configured to detect zero-cross of backelectromotive force of a motor coil provided in a motor; and a controlunit configured to: control driving of the motor by a 1-phaseenergization method by position sensorless driving, perform commutationbased on the zero-cross of the back electromotive force detected by thezero-cross detection unit, control driving of the motor based on arotational speed corresponding to a drive voltage and a load of themotor, and perform extension control of a commutation time for each stepof the motor from a calculated motor deceleration start step until therotational speed of the motor decreases to a predetermined rotationalspeed or less, such that the motor is configured to stop at a desiredstop position when the driving of the motor is stopped.
 2. The motordriving control device according to claim 1, wherein the control unitperforms control of ceasing the commutation based on the zero-cross ofthe back electromotive force from the deceleration start step until themotor is equal to or lower than the predetermined rotational speed toextend the commutation time for each step.
 3. The motor driving controldevice according to claim 2, wherein the control unit increases thecommutation time for each step at a constant rate.
 4. The motor drivingcontrol device according to claim 1, wherein the deceleration start stepis calculated based on a number of driving steps and a number ofdeceleration steps.
 5. The motor driving control device according toclaim 1, further comprising an H-bridge circuit combining half bridgesconnected to the motor coil, and a current detection unit configured todetect a motor current flowing through the motor coil, wherein thecontrol unit specifies a slow decay mode to the H-bridge circuit atevery PWM cycle when the motor current detected by the current detectionunit exceeds a predetermined current value during a period from thedeceleration start step until the motor is stopped.
 6. The motor drivingcontrol device according to claim 5, wherein the control unit repeats acharge mode and the slow decay mode as an operation mode under currentlimitation.
 7. The motor driving control device according to claim 6,wherein the control unit performs transition in order of a shoot throughprotection mode, a flyback mode, and a free mode after repetition of thecharge mode and the slow decay mode at every PWM cycle as the operationmode under current limitation.
 8. A motor driving control methodcomprising: detecting zero-cross of back electromotive force of a motorcoil provided in a motor; and controlling driving of the motor by a1-phase energization method, by position sensorless driving; performingcommutation based on the detected zero-cross of the back electromotiveforce; controlling driving of the motor based on a rotational speedcorresponding to a drive voltage and a load of the motor; and performingextension control of a commutation time for each step of the motor froma calculated motor deceleration start step until the rotational speed ofthe motor decreases to a predetermined rotational speed or less, suchthat the motor is configured to stop at a desired stop position when thedriving of the motor is stopped.